I had the same problem several years ago, but in the servers arena.
in order to solve it I partitioned the solution to two:
1. UNI processors machines
2. SMP processors machines
In UNI processor I created a RT kthread that polls over RTC device.
The observed jitter was 400us.
in SMP processors machines we created a new type of scheduling , called offline. what i did is it to offload a processor and assign it with a task. jitter is 250us under heavy load. solution is open source and can be found at: http://sos-linux.svn.sourceforge.net/viewvc/sos-linux/off...